Mac client for Steam and Epic Games giving away its SDK to Steam devs, Valve also slipped out software developer support for microtransactions, not to mention a 100 fold increase in cloud storage limits (from 1MB to 100MB per game).
Joystiq's PC-centric sister site Big Download noticed the additions in a PDF that Valve recently released on an overview site, detailing the changes coming to the Steam digital distribution client in 2010. As for the microtransaction update, Valve promises users the ability to "buy and instantly use the items they want –- all without leaving the game," perhaps opening up the gate to free-to-play/microtransaction-based games on the service. And, maybe more interestingly, leaving open the possibility of free-to-play games based in the Source and Unreal game engines.
[Via Big Download]